This invention relates generally to test ranges and, more specifically, to radar test ranges.
A radar cross-section (RCS) test range is a facility for measuring the radar scattering properties of test objects, such as aircraft and missiles. Dozens of anechoic chambers and outdoor test ranges have been built over the years to measure target RCS properties. These facilities provide a xe2x80x9cquietxe2x80x9d test zone for measuring the radar signature of a test object. xe2x80x9cQuietxe2x80x9d means that the incident radar wave in the test zone is acceptably free from undesired interference or unwanted reflections from elsewhere in or on the test range.
Because operating conditions of a test range can change with equipment and arrangement of radar absorbers, as well as with time, it is considered good practice to probe the range (test zone) at regular intervals to ensure that radar fields within the test zone behave as expected. However, the time and equipment demanded for field probing put additional cost burdens on the test program. Without a probe of the field, actual measurements on the range remain unquantified.
Though it would be impractical to probe the field everywhere in the test zone, it is generally regarded as acceptable to probe it along a single vertical path and along a single horizontal path that intersect at a nominal center of the target zone. Both paths should be perpendicular to the direction of arrival of the incident wave (i.e., perpendicular to the longitudinal axis of the range).
The classic probe ordinarily used to sample the fields in the target zone is a small active antenna or a small passive reflector (scatterer). In either case, the received probe signal is measured as a function of position across the test zone. It is deemed acceptable to translate the probe along a single horizontal path and along a single vertical path through the target zone.
Active probes (antennas) are mounted on carriages that can be rolled along the floor or ground or that can be jacked up along vertical towers. The probe antenna is indexed along the desired path at discrete intervals, and the position of the probe is read from scales marked on the floor or along the tower. The received signal must be manually recorded for its probe position, so that the signal strength may be charted as a function of the probe position.
One improvement is that the manual procedure is automated by the installation of a set of shaft encoders to continuously report carriage position, whether horizontal or vertical, to a data collection system. However, because the carriage systems are physically large and robust, it takes much time and effort to assemble them, and radar reflections from their sheer bulk tend to contaminate the test zone being probed.
An alternative to current carriage systems is to use a passive scatterer installed on a low-reflection target support device, such as a pylon or a plastic-foam tower. The signal received by the facility""s resident echo-measuring instrumentation system is measured as a function of position across the test zone. However, the target support device contaminates the measurement. This contamination is especially severe at lower radar frequencies.
Thus, there is an unmet need for a fast, accurate, and more cost effective method of performing a field probe.
The present invention allows probing incident radar fields in a target test zone of a radar cross-section (RCS) test facility in a fraction of the time that is used by conventional methods. The present invention accomplishes probing by exploiting angular radar response of a string or wire stretched horizontally or vertically through the test zone. One end of the string is fixed, while the other end is moved by a wall-mounted or floor-mounted actuator. Thus, the angle of the string is gradually changed with respect to the direction of arrival of the incident wave. The radar echo from the string is measured as a function of the string angle. The data is then processed to yield a profile of the incident wave intensity along the string. This probing can be routinely achieved for any desired frequency.
The radar echo includes an in-phase component and a quadrature component. In order to yield a profile of the incident wave intensity Fast Fourier Transforms of the in-phase and quadrature components are taken.
In one aspect of the invention, the radar test zone is in an indoor or outdoor radar test range.